TECHNICAL FIELD
[0001] The present invention relates to a spherical crystalline silica powder and a method
for producing the same.
BACKGROUND
[0002] Silica powders are widely used as fillers for resins. In particular, spherical silica
powders can be filled to high degree with good dispersibility in resins, and therefore,
are used preferably as sealing material fillers for semiconductor elements. Sealing
material fillers for semiconductor elements preferably have a high coefficient of
thermal expansion so as to prevent the occurrence of warping or cracking in the sealing
material due to temperature changes during reflow or temperature changes during temperature
cycle tests, etc. However, spherical silica powders produced by a flame fusion method,
which is one method for producing a spherical silica powder, are amorphous and therefore,
tend to have a low coefficient of thermal expansion. Here, attempts have been made
to improve the coefficient of thermal expansion and the thermal conductivity of spherical
amorphous silica powders by heating at a high temperature to crystallize the amorphous
silica powders (for example, Patent Document 1).
It is known that crystalline silica powders take on different crystal structures depending
on pressure and temperature. Examples of crystal structures of crystalline silica
powders include a-quartz, cristobalite, and tridymite. Patent Document 2 discloses
a silica powder having two or more kinds of crystal forms selected from α-quartz,
tridymite, and cristobalite.
[0003] Note that accompanying an increase in information communication volumes in the communications
field, the application of high-frequency bands in electronic instruments and communication
instruments, etc., has become more widespread. Accompanying the application of high-frequency
bands, materials having a low dielectric tangent are demanded in order to prevent
circuit signal transmission losses. Patent Document 3 proposes obtaining a spherical
amorphous silica with a reduced dielectric tangent by heat treating, at a prescribed
temperature for a prescribed time, a spherical amorphous silica powder obtained by
a powder melting method.
Patent Document 1: WO 2016/031823 A
Patent Document 2: JP 2005-231973 A
Patent Document 3: JP 2021-38138 A
SUMMARY OF INVENTION
[0004] The problem of the present invention is to provide: a spherical crystalline silica
powder which enables a resin molded article having a high coefficient of linear thermal
expansion and a low dielectric tangent to be obtained; and a method for producing
the same.
[0005] The present inventors discovered that by crystallizing a spherical amorphous silica
powder, then bringing into contact with an acid and further subjecting to a heat treatment,
it is possible to obtain a spherical crystalline silica powder having a high coefficient
of linear thermal expansion and a further reduced dielectric tangent, and that the
number of water molecules desorbed at 50°C-1,000°C in the obtained spherical crystalline
silica powder is 10 µmol/g or less, which led to the completion of the present invention.
[0006] The present invention has the following embodiments.
- [1] A spherical crystalline silica powder in which the number of water molecules desorbed
at 50°C-1,000°C when the temperature is increased from 25°C to 1,000°C at a condition
of 30°C/min. is 10 µmol/g or less, and
in which 10 mass% or more of the total powder is α-quartz crystal.
- [2] The spherical crystalline silica powder described in [1], wherein the degree of
crystallization of the total powder, as measured by an X-ray diffraction method, is
30-98%.
- [3] The spherical crystalline silica powder described in [1] or [2], wherein 20-90
mass% of the total powder is α-quartz crystal.
- [4] The spherical crystalline silica powder described in any one of [1] to [3], wherein
0-70 mass% of the total powder is cristobalite crystal.
- [5] The spherical crystalline silica powder described in any one of [1] to [4], wherein
the content of alkaline-earth metal elements therein is less than 10,000 µg/g by oxide
conversion.
- [6] A resin composition comprising the spherical crystalline silica powder described
in any one of [1] to [5], and a resin.
- [7] A method for producing a spherical crystalline silica powder, the method comprising:
- (i) heating a spherical amorphous silica powder to obtain a spherical crystalline
silica powder;
- (ii) bringing the spherical crystalline silica powder into contact with an acid; and
- (iii) heating, at 800-1,400°C, the spherical crystalline silica powder treated by
(ii).
- [8] The production method described in [7], wherein the spherical crystalline silica
powder is obtained by heating a mixture of a spherical amorphous silica powder and
a solvent in (i).
[0007] According to the present invention it is possible to provide: a spherical crystalline
silica powder which enables a resin molded article having a high coefficient of linear
thermal expansion and a low dielectric tangent to be obtained; and a method for producing
the same.
BRIEF DESCRIPTION OF DRAWINGS
[0008] Fig. 1 is a graph showing the thermal expansion behavior, as measured by thermomechanical
analysis (TMA), of test pieces comprising a silica powder of Example 1-5, Comparative
Example 1-1 (amorphous silica powder), Comparative Example 1-3 (spherical cristobalite
crystal), or a reference example (ground quartz).
DESCRIPTION OF EMBODIMENTS
[0009] Hereinafter, embodiments of the present invention will be described in detail. The
present invention is not limited to the following embodiments and can be carried out
with modifications, as appropriate, as long as the effects of the invention are not
inhibited. Note that herein, "-" with regard to numerical ranges means "... or more
and ... or less". For example, "X-Y" means X more and Y or less. Note that herein,
a "powder" means an "aggregate of particles".
[Spherical crystalline silica powder]
[0010] In the spherical crystalline silica powder according to the present embodiment, the
number of water molecules desorbed at 50°C-1,000°C when the temperature is increased
from 25°C to 1,000°C at a condition of 30°C/min (hereinafter also referred to simply
as the "number of desorbed water molecules" or the "number of desorbed H
2O molecules") is 10 µmol/g or less, and 10 mass% or more of the total powder is α-quartz
crystal.
[0011] "Spherical" means having a projected view with a shape close to circular when observed
with a microscope, or the like. Due to being spherical, the powder can be filled at
a high content in a resin without fluidity being reduced. Average circularity and
a method for measuring the same will be described later.
[0012] "Crystalline" here means that the degree of crystallization is 20% or more. A method
for measuring the degree of crystallization will be described later. Conventionally,
attempts to crystallize a spherical amorphous silica powder have involved trying to
raise thermal conductivity by configuring the degree of crystallization to be 80%
or more (for example, Patent Documents 1 and 2). However, it was discovered that,
surprisingly, a spherical crystalline silica which has a number of desorbed water
molecules of 10 µmol/g or less and in which 10 mass% or more of the total powder is
α-quartz crystal, irrespective of the degree of crystallization (in both cases in
which the degree of crystallization is less than 80% and cases in which the degree
of crystallization exceeds 80%), enables a resin molded article having a low dielectric
tangent and a high coefficient of linear thermal expansion to be obtained.
[0013] The "number of desorbed water molecules" was measured by using a Pyrolyzer GC/MS
system (comprising a combination of a gas chromatography mass spectrometer (JMS-Q1500GC)
manufactured by JEOL Ltd., and a multi-shot pyroloyzer (EGA/PY-3030D) manufactured
by Frontier Laboratories, Ltd.), increasing the temperature from 25°C to 1,000°C at
30°C/min., and measuring an area value of an obtained mass chromatogram (m/z=18) in
a 50°C-1,000°C range. The number of desorbed water molecules was calculated from the
measured area value by drawing a calibration curve using a standard substance with
a known amount of dehydration.
[0014] In one embodiment, the number of desorbed H
2O molecules is preferably less than 10 µmol/g, more preferably 9 µmol/g or less, even
more preferably 8.8 µmol/g or less, and particularly preferably 8.5 µmol/g or less.
[0015] In one embodiment, the number of desorbed H
2O molecules is preferably less than 10 µmol/g, more preferably 8 µmol/g or less, even
more preferably 6 µmol/g or less, and particularly preferably 4 µmol/g or less.
[0016] An example of a method for rendering the number of desorbed water molecules so as
to be 10 µmol/g or less is a method involving crystallizing a spherical amorphous
silica powder, and then performing a step for bringing the powder into contact with
an acid and further subjecting to a heat treatment. The details of the production
method will be described later.
[0017] By adjusting the temperature or time of the crystallization step, the amount of hydroxyl
groups in the surface of the powder can be reduced and thereby it is possible to reduce
the number of desorbed water molecules. However, as described above, the crystal form
of the spherical crystalline silica powder changes depending on the heating temperature
during crystallization, etc., and therefore, there are times when a suitable crystal
phase cannot be controlled in the case of a temperature for reducing the hydroxyl
groups in the surface of the powder becoming high or a time for reducing the hydroxyl
groups in the surface of the powder becoming long. Further, the dielectric tangent
of the resin molded article may become high.
[0018] The degree of crystallization of the total spherical crystalline silica powder (hereinafter
also referred to simply as the "degree of crystallization"), as measured by an X-ray
diffraction method, is preferably 30-98%, more preferably 35-90%, even more preferably
38-85%, and even further preferably 38-80%. By configuring the degree of crystallization
so as to be 30-98%, a spherical crystalline silica powder having a high coefficient
of linear thermal expansion can easily be obtained. The degree of crystallization
is calculated from a ratio of the integral area of a peak of a reference crystalline
silica measured by X-ray diffraction (XRD) and an integral area of a peak of the spherical
crystalline silica (integral area of peak of spherical crystalline silica/integral
area of peak of reference crystalline silica).
[0019] The degree of crystallization can be adjusted by adjusting the temperature and/or
time in the step of crystallizing the spherical amorphous silica powder. Further,
the degree of crystallization can also be adjusted by adjusting the temperature and/or
time in the step of further heating the powder after crystallization. The degree of
crystallization becomes higher with a higher temperature and with a longer time. The
preferred temperatures and/or times in the crystallization step and the heating step
are described below. Furthermore, it is possible to adjust the degree of crystallization
by using a crystallizing agent described later. When the degree of crystallization
is adjusted by temperature or time, there are times when it is difficult to control
a suitable crystal phase. Therefore, from the perspective of facilitating control
of the crystal phase, it is preferable to adjust the degree of crystallization by
using the crystallizing agent described later.
[0020] From the viewpoint of reducing viscosity when mixed in a resin, the average circularity
of the spherical crystalline silica powder is preferably 0.80 or more, more preferably
0.85 or more, and even more preferably 0.90 or more.
[0021] The method for measuring the "average circularity" is as described below. After fixing
the spherical crystalline silica powder with a carbon tape, an osmium coating is applied.
Thereafter, the powder is photographed at a magnification of 500-50,000 using a scanning
electron microscope, a projected area (S) and a projected perimeter (L) of a particle
constituting are calculated using an image analysis device, and then the circularity
is calculated from formula (1) below. Circularities are calculated for 200 arbitrary
particles and the average value thereof is used as the average circularity.

[0022] 10 mass% or more of the total spherical crystalline silica powder is α-quartz crystal,
preferably 20 mass% or more of the total spherical crystalline silica powder is α-quartz
crystal, and more preferably 30 mass% or more of the total spherical crystalline silica
powder is α-quartz crystal.
[0023] By comprising 10 mass% or more of α-quartz crystal, it is possible to obtain a resin
molded article having a high coefficient of linear thermal expansion and a low dielectric
tangent. Further, thermal expansion behavior close to that of a ground quartz powder
can be demonstrated when configured as resin molded article. A ground quartz powder
has little dimensional change due to thermal expansion at the reflow temperature vicinity
when configured as a resin molded article. Due thereto, it is possible to easily suppress
cracking and warping, etc., of the molded article caused by temperature changes before
and after a reflow process.
[0024] In one embodiment, 40 mass% or more of the total spherical crystalline silica powder
may be α-quartz crystal, and 45 mass% or more of the total spherical crystalline silica
powder may be α-quartz crystal.
[0025] In one embodiment, preferably 20-90 mass% of the spherical crystalline silica powder
is α-quartz crystal, more preferably 25-85 mass% of the total spherical crystalline
silica powder is α-quartz crystal, and even more preferably 30-70 mass% of the total
spherical crystalline silica powder is α-quartz crystal.
[0026] Preferably 0-70 mass% of the total spherical crystalline silica powder is cristobalite
crystal, more preferably 0-50 mass% of the total spherical crystalline silica powder
is cristobalite crystal, even more preferably 0-40 mass% of the total spherical crystalline
silica powder is cristobalite crystal, and particularly preferably 0-36 mass% of the
total spherical crystalline silica powder is cristobalite crystal. The spherical crystalline
silica powder does not have to comprise cristobalite crystal. In the case of comprising
cristobalite crystal, by configuring the content thereof to be 70 mass% or less, a
resin molded article having a high coefficient of linear thermal expansion and a low
dielectric tangent can be produced more easily.
[0027] Preferably 0-70 mass% of the total spherical crystalline silica powder is tridymite
crystal and more preferably 0-40 mass% of the total spherical crystalline silica powder
is tridymite crystal. The spherical crystalline silica powder does not have to comprise
tridymite crystal. In the case of comprising tridymite crystal, by configuring the
content thereof to be 70 mass% or less, a resin molded article having a high coefficient
of linear thermal expansion and a low dielectric tangent can be produced more easily.
[0028] The content of each crystalline form in the spherical crystalline silica powder can
be measured by X-ray diffraction measurement and analyzed by Rietveld analysis.
[0029] The average particle diameter (volume-based cumulative 50% diameter D
50) of the spherical crystalline silica powder is preferably 0.1-100 µm, more preferably
0.2-50 µm, and even more preferably 0.3-10 µm. By configuring the average particle
diameter of the spherical crystalline silica powder so as to be 0.1-100 µm, filling
properties in a resin are likely to be better. "Volume-based cumulative 50% diameter
D
50" means a particle diameter corresponding to a cumulative value of 50% in a volume-based
cumulative particle size distribution measured by using a laser diffraction particle
size distribution measuring device (refraction index: 1.50).
[0030] The specific surface area of the spherical crystalline silica powder is preferably
less than 6 m
2/g, more preferably 5.5 m
2/g or less, and even more preferably 5 m
2/g or less. By configuring the specific surface area of the spherical crystalline
silica powder so as to be 6 m
2/g or less, it is easy to achieve a lower dielectric tangent. Note that the lower
limit of the specific surface area of the spherical crystalline silica powder is preferably
no less than 1 m
2/g.
[0031] In one embodiment, the specific surface area of the spherical crystalline silica
powder may be 1-6 m
2/g. Note that the specific surface area of the spherical crystalline silica powder
indicates a value measured according to the single point BET method by using a fully
automated specific surface area and diameter measuring device.
[0032] When producing the spherical crystalline silica powder, an alkali metal compound
or an alkaline earth metal compound, etc., may be used as a crystallizing agent with
an objective of promoting crystallization. From the viewpoint of further reducing
the dielectric tangent, the content of alkaline earth metal elements (Be, Mg, Ca,
Sr, Ba, etc.) remaining in the powder is, by oxide conversion, preferably less than
10,000 µg/g and more preferably less than 9,000 µg/g. The content of alkali metal
elements (Li, Na, etc.) remaining in the powder is, by oxide conversion, preferably
less than 30,000 µg/g.
[0033] The content (oxide conversion) of the alkali metal compounds and the alkaline earth
metal elements in the spherical crystalline silica powder is measured by using an
ICP optical emission spectrometer.
[0034] From the viewpoint of reducing impurities, it is preferable for the spherical crystalline
silica powder to have a content of U of 10 ppb or less, a content of Th of 20 ppb
or less, a content of Fe of 200 ppb or less, and/or a content of Al of 1 mass% or
less (10,000 ppm or less). The content of the above impurities in the spherical crystalline
silica powder is measured by using an ICP optical emission spectrometer.
[0035] In a test piece (resin molded article) made using the spherical crystalline silica
powder by the method described below, the coefficient of linear thermal expansion
(CTE1) at or below a glass transition temperature Tg is preferably 3.5×10
-5/K-4.5×10
-5/K, more preferably 3.7×10
-5/K-4.3×10
-5/K, and even more preferably 3.8×10
-5/K-4.0×10
-5/K. Since the coefficient of linear thermal expansion (CTE1) at or below the glass
transition temperature Tg is high, it is possible to prevent warping and cracking
during a temperature cycle when a product is used.
[0036] In a test piece (resin molded article) made using the spherical crystalline silica
powder by the method described below, the coefficient of linear thermal expansion
(CTE2) in a temperature region exceeding the temperature glass transition temperature
Tg is preferably 10.0×10
-5/K-11.5×10
-5/K, more preferably 10.5×10
-5/K-11.3×10
-5/K, and even more preferably 10.6×10
-5/K-11.1×10
-5/K. Since the coefficient of linear thermal expansion (CTE2) in a temperature region
exceeding the glass transition temperature Tg is high, it is possible to prevent warping
and cracking during reflow.
[0037] As a method for making test pieces, a liquid-state epoxy resin (for example "JER
828" manufactured by Mitsubishi Chemical Corporation) and a hardening agent (4,4-Diaminodiphenylmethane)
are mixed at a weight ratio of 4:1, a spherical crystalline silica powder is mixed
so as to be 40 vol.% thereof, and the mixture is cured at 200°C to make a cured body.
The cured body is processed to a test piece with a size of 4 mm × 4 mm × 15 mm.
[0038] The method for measuring the coefficients of linear thermal expansion CTE1, CTE2
is performed using a thermal mechanical analysis device in conditions with a measurement
range of -10°C-270°C and a temperature increase rate of 5°C/minute, and the coefficient
of linear thermal expansion (CTE1) at or below the glass transition temperature Tg
and the coefficient of linear thermal expansion (CTE2) in a temperature region exceeding
the glass transition temperature Tg are calculated.
[0039] The dielectric tangent of a resin sheet made using the spherical crystalline silica
powder by the method described later is preferably 7.0×10
-4 or less, more preferably, 6.9×10
-4 or less, and even more preferably 6.8×10
-4 or less. By configuring the dielectric tangent (tanδ) so as to be 7.0×10
-4 or less, it is possible to more effectively prevent circuit signal transmission losses
in electronic instruments and communication instruments having a high-frequency band
applied therein.
[0040] The dielectric constant (εr) of a resin sheet made using the spherical crystalline
silica powder by the method described later is preferably 2.5 or more, more preferably
2.6 or more, and even more preferably 2.65 or more. By configuring the dielectric
constant (εr) so as to be 2.5 or more, the dielectric constant becomes higher and
electronic instruments and communication instruments, etc., can be further miniaturized.
[0041] It was discovered that by crystallizing a spherical amorphous silica powder, then
bringing into contact with an acid and further subjecting to a heat treatment, it
is possible to obtain a spherical crystalline silica powder having a high coefficient
of linear thermal expansion and a further reduced dielectric tangent.
[0042] The method for making resin sheets involves obtaining a resin composition by mixing
a polyethylene resin powder and a spherical crystalline silica powder such that the
content of the spherical crystalline silica powder filled therein is 40 vol.%, loading
the obtained resin composition into a 3 cm-diameter metal frame at an amount such
that the thickness thereof is approximately 3 mm, rendering into a sheet by a nanoimprinting
device, and cutting the obtained sheet into 1.5 cm × 1.5 cm sizes to obtain resin
sheets for testing.
[0043] The method for measuring the dielectric constant and dielectric tangent involves
connecting a 36 GHz cavity resonator to a vector network analyzer, arranging a resin
sheet for testing so as to cover a 10 mm-diameter hole provided in the cavity resonator,
and measuring a resonance frequency (f0) and an unloaded Q value (Qu). The same measurement
is repeated five times with the evaluation sample being rotated 90 degrees after each
measurement, and average values of the obtained f0 and Qu values are used as measured
values. Analytical software is used to calculate the dielectric constant from f0 and
the dielectric tangent (tan δc) from Qu. Note that as measurement conditions, measurement
temperature is 20°C and humidity is 60%RH.
[0044] The thermal conductivity of the spherical crystalline silica powder, measured in
a resin sheet made by the method described later, is preferably 0.48 W/mK or more,
more preferably 0.50 W/mK or more, and even more preferably 0.55 W/mK or more. By
configuring the thermal conductivity so as to be 0.48 W/mK or more, the thermal conductivity
of the fabricated resin sheets can be improved.
[0045] The thermal conductivity can be improved by crystallizing a spherical amorphous silica
powder. It was discovered that after crystallization, by bringing the silica powder
into contact with an acid and subjecting to a heat treatment, the thermal conductivity
is further improved.
[0046] Thermal conductivity is a value calculated by multiplying the thermal diffusivity,
measured by the method described below, by specific gravity and specific heat.
[0047] The thermal diffusivity was determined by a laser flash method using a processed
resin sheet. A xenon flash analyzer (product name: LFA 447 NanoFlash; manufactured
by Netzsch) was used as the measurement device. As a method for making resin sheets,
a liquid-state epoxy resin (for example, "JER 828" manufactured by Mitsubishi Chemical
Corporation) and a hardening agent (4,4-Diaminodiphenylmethane) are mixed at a weight
ratio of 4:1, a spherical crystalline silica powder is filled so as to be 40 vol.%
thereof, and the mixture is cured at 200°C to make a cured body. The cured body is
processed to a disk-shaped test piece having a diameter of 10 mm × a thickness of
1 mm.
[0048] The specific gravity of the powder was determined by using the Archimedes method.
[0049] The specific heat was determined by using a differential scanning calorimeter (product
name: Q2000; manufactured by TA Instruments) and increasing the temperature from room
temperature to 200°C at a temperature increase rate of 10°C/minute in a nitrogen atmosphere.
(Use)
[0050] The spherical crystalline silica powder according to the present embodiment can be
filled at a high content and with good dispersibility in a resin, and therefore, can
be used as filler of resin molded articles for various uses such as electronic instruments
and communication instruments, etc. In particular, since it is possible to obtain
a resin molded article having a high coefficient of thermal expansion and a low dielectric
tangent, the spherical crystalline silica powder according to the present embodiment
can be preferably used to produce a semiconductor sealing material for electronic
instruments and communication instruments, etc., which have a high-frequency band
applied therein. A resin molded article comprising the spherical crystalline silica
powder can suppress cracking and warping, etc., in temperature cycles during use and
temperature changes before and after a reflow process.
[Production Method]
[0051] The method for producing the spherical crystalline silica powder according to the
present embodiment comprises:
- (i) heating a spherical amorphous silica powder to obtain a spherical crystalline
silica powder;
- (ii) bringing the spherical crystalline silica powder into contact with an acid; and
- (iii) heating, at 800-1,400°C the spherical crystalline silica powder treated by (ii).
[0052] The production method may also comprise a step (i') of preparing a spherical amorphous
silica powder before step (i).
<Step (i'): spherical amorphous silica powder preparation step>
[0053] In step (i'), which the production method may comprise arbitrarily, a spherical amorphous
silica powder is prepared. As the spherical amorphous silica powder, it is possible
to use a powder produced by a conventional and publicly-known method. However, from
the viewpoints of productivity and production cost, it is preferable to use a spherical
amorphous silica powder produced by a flame fusion method. In a flame fusion method,
an ore powder is sprayed into a high-temperature flame formed by a combustible gas
and a supporting gas by using a burner and fused and spheroidized at a temperature
equal to or higher than the ore powder melting point (for example, a temperature of
1,800°C or more).
[0054] From the viewpoint of cost reduction, the raw material is preferably a mineral and/or
ore ground product. Examples of the mineral or ore include silica sand and silica
stone. The average particle diameter of the raw material is not limited and may be
selected, as appropriate, from the viewpoint of workability.
[0055] The average particle diameter (volume-based cumulative 50% diameter D
50) of the raw material is preferably 0.1-100 µm, more preferably 0.2-50 µm, and even
more preferably 0.3-10 µm.
[0056] The obtained spherical amorphous silica powder is classified as necessary.
[0057] The average circularity of the spherical amorphous silica powder is preferably 0.80
or more, more preferably 0.85 or more, and even more preferably 0.90 or more. The
method for measuring the average circularity is as described above.
[0058] The average particle diameter (volume-based cumulative 50% diameter D
50) of the spherical amorphous silica powder is preferably 0.1-100 µm, more preferably
0.2-50 µm, and even more preferably 0.3-10 µm.
<Step (i): crystallization step>
[0059] In step (i), the spherical amorphous silica powder is heated to obtain a spherical
crystalline silica powder. The spherical amorphous silica powder is crystallized by
being heated at a prescribed temperature to obtain a crystalline silica powder. In
order for 10 mass% or more of the total powder to become α-quartz crystal, the heating
temperature is preferably 900-1,250°C, more preferably 950-1,200°C, and even more
preferably 1,000-1,200 °C. The heating time is preferably 2-40 hours, more preferably
3-30 hours, and even more preferably 4-24 hours. The heating method is not particularly
limited and may be performed with a publicly-known electric furnace, or the like.
Thereafter, the powder is cooled to an ambient temperature (26°C).
[0060] The spherical crystalline silica powder enables a resin molded article having a high
coefficient of linear thermal expansion and a low dielectric tangent to be obtained
even with a lower degree of crystallization than conventional, and therefore, the
crystallization step can be performed under conditions that are more moderate than
those conventionally used (low temperature and/or short time).
[0061] It is possible to use a crystallizing agent with an objective of promoting crystallization.
Examples of the crystallizing agent include oxides and carbonates, etc., of alkali
metals or alkaline earth metals. Specific examples of the crystallizing agent include
MgCOs, CaCOs, SrCOs, Li
2O, Na
2O, etc., and it is preferable to use one or more crystallizing agents selected therefrom.
When a crystallizing agent is used, the raw material spherical amorphous silica powder
and the crystallizing agent are mixed (for example, mixing for 2-10 minutes using
a grinder such as a vibrating mill or some kind of mixer, etc.), and thereafter heated
in an electric furnace, or the like.
[0062] The proportion at which the crystallizing agent is used is preferably 1-10 moles,
more preferably 2-8 moles, and even more preferably 3-5 moles with respect to 100
moles of the spherical amorphous silica powder.
[0063] In step (i), the amorphous silica powder (preferably, a mixture of the spherical
amorphous silica powder and a crystallizing agent) may be mixed with a solvent and
thereafter heated to obtain a spherical crystalline silica powder. By heating the
mixture of the spherical amorphous silica powder and the solvent, the degree of crystallization
and the crystal form can be easily adjusted. Examples of the solvent include water
and alcohol. The amount of solvent used may be 1-30 ml with respect to 10 g of the
spherical amorphous silica powder.
[0064] After being crystallized, the silica powder can, as necessary, be crushed and classified
by using a vibrating sieve, etc.
<Step (ii): contact with acid step>
[0065] In step (ii), the spherical crystalline silica powder is brought into contact with
an acid. Examples of the acid include acids with an acid dissociation constant pK
a at 25°C of 7.0 or less, preferably or 6.0 or less, and more preferably of 5.0 or
less. Specific examples of the acid include acetic acid, nitric acid, hydrochloric
acid, phosphoric acid, and sulfuric acid, etc., and it is preferable to use one or
more acids selected therefrom.
[0066] The amount of acid used, for example, may be 50-1,000 ml and may be 100-500 ml with
respect to 10 g of the spherical crystalline silica powder.
[0067] The method for bringing the spherical crystalline silica powder into contact with
the acid is not particularly limited and may, for example, be performed by adding
the acid to the spherical crystalline silica powder and mixing.
[0068] The mixing method is not particularly limited and may, for example, be performed
by putting the spherical crystalline silica powder and an acid aqueous solution into
a beaker and stirring at 10-90°C (preferably 30-70°C) for 10-600 minutes (preferably
30-180 minutes).
[0069] Thereafter, the mixture is washed a plurality of times using water or ethanol and
filtered to remove the acid, and the obtained powder is heated in step (iii).
<Step (iii): heating step>
[0070] In step (iii), after undergoing the treatment in step (ii), the spherical crystalline
silica powder is heated at 800-1,400°C. The heating temperature is preferably 900-1,300°C
and more preferably 1,000-1,200°C. By heating the spherical crystalline silica powder
at 800-1,400°C, the number of desorbed water molecules can be reduced without significantly
influencing the content of the α-quartz crystal and cristobalite crystal. Further,
the degree of crystallization can be adjusted easily.
[0071] The heating time is preferably 30 minutes-24 hours, more preferably 1-12 hours, and
even more preferably 2-8 hours. The heating method is not particularly limited and
a publicly-known electric furnace, or the like, may be used.
[0072] After allowing to cool naturally inside the electric furnace, the spherical crystalline
silica powder is recovered in a state of 110°C-300°C and further cooled to 25°C in
an environment with a humidity of 40%RH or less.
[0073] The method may comprise, after step (iii), a step of classifying so as to achieve
a desired average particle diameter.
[0074] The number of desorbed water molecules, the degree of crystallization, the crystal
form, the average particle diameter (volume-based cumulative 50% diameter D
50), the average circularity, and the impurity content, etc., of the obtained spherical
crystalline silica powder are as described above, and therefore, descriptions thereof
are omitted here.
[0075] [Resin Composition] The resin composition according to the present embodiment comprises
the spherical crystalline silica powder described above and a resin.
(Resin)
[0076] Examples of the resin include thermoplastic resins and thermosetting resins. Examples
of the resin include: polyethylene resins; polypropylene resins; epoxy resins; silicone
resins; phenol resins; melamine resins; urea resins; unsaturated polyester resins;
fluorine resins; polyamide-based resins such as polyimide resins, polyamide imide
resins, and polyether imide resins; polyester-based resins such as polybutylene terephthalate
resins and polyethylene terephthalate resins; polyphenylene sulfide resins; fully
aromatic polyester resins; polysulfone resins; liquid crystal polymer resins; polyether
sulfone resins; polycarbonate resins; maleimide modified resins; ABS resins; AAS (acrylonitrile-acrylic
rubber-styrene) resins; and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene)
resins. The foregoing may be used alone or as a combination of two or more.
[0077] When the resin composition is to be used as a high-frequency band substrate or an
insulating material, it is possible to employ a publicly-known low-dielectric resin
material that is used in such a use. Specifically, it is possible to use at least
one resin selected from hydrocarbon-based elastomer resins, polyphenylene-ether resins,
and aromatic polyene-based resins. Among the foregoing, a hydrocarbon-based elastomer
resin or polyphenylene-ether resin is preferable. The ratio of the foregoing resins
is preferably 20-95 mass% and more preferably 30-95 mass% with respect to the total
mass of the resin composition.
[0078] The content of the spherical crystalline silica powder in the resin composition is
not particularly limited and may be adjusted, as appropriate, according to objectives.
For example, when applied in a high-frequency substrate material or an insulating
material use, the spherical crystalline silica powder may be blended in the range
of 5-80 mass% and more preferably in the range of 5-70 mass% with respect to the total
mass of the resin composition.
[0079] The blending ratios of the resin and the spherical crystalline silica powder in the
resin composition can be adjusted, as appropriate, in accordance with targeted dielectric
properties such as the coefficient of linear thermal expansion and the dielectric
tangent. For example, the amount of the resin can be adjusted in the range of 10-10,000
parts by mass with respect to 100 parts by mass of the spherical crystalline silica
powder.
[0080] In a range that does not hinder the effects of the present invention, the resin composition
may have a hardening agent, a hardening accelerator, a mold release agent, a coupling
agent, a coloring agent, or the like, blended therein.
[Method for producing resin composition]
[0081] The method for producing the resin composition is not particularly limited, and the
resin composition may be produced, for example, by stirring, dissolving, mixing, and
dispersing prescribed amounts of each material. The devices used for mixing, stirring,
and dispersing, etc., the mixture are not particularly limited, and it is possible
to use a grinding machine, a three-roller miller, a ball mill, a planetary mixer,
etc., provided with a device for stirring and heating. Further, the foregoing devices
may be used in combination, as appropriate.
[0082] As described above, resin compositions comprising the spherical crystalline silica
powder according to the present embodiment can achieve a high coefficient of linear
thermal expansion and a low dielectric tangent. Due thereto, resin compositions comprising
the spherical crystalline silica powder according to the present embodiment can be
preferably used to produce semiconductor sealing materials for electronic instruments
and communication instruments, etc., which have a high-frequency band applied therein.
Obtained resin molded articles can suppress cracking and warping, etc., in temperature
cycles during use and temperature changes before and after a reflow process.
EXAMPLES
[0083] The present invention shall be explained in more detail by referring to the examples
below, but interpretation of the present invention is not to be limited by these examples.
[0084] [Reference example] 10 g of a ground quartz powder ("silicon dioxide 99.9%" manufactured
by Fujifilm Wako Pure Chemical Corporation, average particle diameter D
50: 20.7 µm) was put into an alumina crucible and subjected to a heat treatment for
four hours at an electric furnace internal temperature of 1,000°C. After the heat
treatment, the mixture was cooled to 200°C inside the furnace, then cooled to room
temperature in a desiccator (23°C-10%RH), and the powder thus obtained was used as
the silica powder of the reference example.
Experiment 1
[Example 1-1]
[0085] A spherical amorphous silica powder ("FB-5D" manufactured by Denka Co., Ltd., average
particle diameter D
50: 4.5 µm) and CaCOs were weighed so that the molar ratio (SiO
2:CaCO
3) was 100:3 and dry-blended for three minutes in a vibration mixer (manufactured by
Resodyn Corporation). 50 g of the mixture was put into an alumina crucible, then 5
ml of pure water was added thereto and mixed. Thereafter, the crucible was placed
in an electric furnace and subjected to a heat treatment for 12 hours with an electrical
furnace interior temperature of 1,000°C (step (i)). After the heat treatment, the
mixture was cooled to 200°C inside the furnace, then cooled to room temperature in
a desiccator (23°C-10%RH), and the powder thus obtained was crushed using a mortar
and classified with a sieve having a mesh size of 200 µm.
[0086] The obtained powder was put in a 500 ml beaker, 500 ml of 1M acetic acid was added
dropwise thereto, and stirred and mixed for 60 minutes (step (ii)). Thereafter, the
mixture was filtered to remove the acetic acid, the obtained residue was put in an
alumina crucible, placed in an electric furnace, and subjected to a heat treatment
for four hours with an electric furnace interior temperature of 1,000°C (step (iii)).
After the heat treatment, the mixture was cooled to 200°C inside the furnace and then
cooled to room temperature in a desiccator (23°C-10%RH) to obtain the spherical crystalline
silica powder of Example 1-1.
[Example 1-2]
[0087] Other than setting the heating temperature in step (iii) to 1,200°C, the spherical
crystalline silica powder of Example 1-2 was obtained by the same method as in Example
1-1.
[Example 1-3]
[0088] Other than weighing the spherical amorphous silica powder and the CaCOs in step (i)
so that the molar ratio thereof was 100:5 and setting the heating temperature in step
(iii) to 1,100°C, the spherical crystalline silica powder of Example 1-3 was obtained
by the same method as in Example 1-1.
[Example 1-4]
[0089] Other than weighing the spherical amorphous silica powder and the CaCOs in step (i)
so that the molar ratio thereof was 100:5 and setting the heating temperature in step
(iii) to 1,200°C, the spherical crystalline silica powder of Example 1-4 was obtained
by the same method as in Example 1-1.
[Example 1-5]
[0090] Other than setting the heat treatment conditions in step (i) so as to be 1,200°C
for 24 hours and using 500 ml of 1M nitric acid instead of the acetic acid in step
(ii), the spherical crystalline silica powder of Example 1-5 was obtained by the same
method as in Example 1-1.
[Comparative Example 1-1]
[0091] A spherical amorphous silica powder ("FB-5D" manufactured by Denka Co., Ltd, average
particle diameter D
50: 4.5 µm) was used as the silica powder of Comparative Example 1 (that is, steps (i)-(iii)
were not carried out).
[Comparative Example 1-2]
[0092] 10 g of the spherical amorphous silica powder of Comparative Example 1-1 was filled
in an alumina crucible and subjected to a heat treatment for four hours with an electric
furnace interior temperature of 1,000°C. After the heat treatment, the mixture was
cooled to 200°C inside the furnace and then cooled to room temperature in a desiccator
(23°C-10%RH) to obtain the silica powder of Comparative Example 1-2. Note that when
the degree of crystallization was measured using the method described later, the silica
powder of Comparative Example 1-2 had the same degree of crystallization as Comparative
Example 1-1, crystallization had not proceeded, and the silica powder had remained
amorphous.
[Comparative Example 1-3]
[0093] A spherical amorphous silica powder ("FB-5D" manufactured by Denka Co., Ltd., average
particle diameter D
50: 4.5 µm) and CaCOs were weighed so that the molar ratio (SiO
2:CaCO
3) was 100:1 and dry-blended for three minutes in a vibration mixer (manufactured by
Resodyn Corporation). The mixture was put in a crucible, placed in an electric furnace,
the temperature was increased in air at a temperature increase rate of 10°C/min. to
1,300°C, and kept at 1,300°C for four hours (step (i)). The mixture was allowed to
cool naturally to an ambient temperature in the furnace to obtain the silica powder
of Comparative Example 1-3.
Experiment 2
[0094] [Example 2-1] A spherical amorphous silica powder ("SFP-30M" manufactured by Denka
Co., Ltd., average particle diameter D
50: 0.68 µm) and CaCOs were weighed so that the molar ratio (SiO
2:CaCO
3) was 100:3 and dry-blended for three minutes in a vibration mixer (manufactured by
Resodyn Corporation). 50 g of the mixture was put into an alumina crucible, and 5
ml of pure water was added thereto and mixed. Thereafter, the crucible was placed
in an electric furnace and subjected to a heat treatment for 12 hours with an electrical
furnace interior temperature of 1,100°C (step (i)). After the heat treatment, the
mixture was cooled to 200°C inside the furnace, then cooled to room temperature in
a desiccator (23°C-10%RH), and the powder thus obtained was crushed using a mortar
and classified with a sieve having a mesh size of 200 µm.
[0095] The obtained powder was put in a 500 ml beaker, 500 ml of 1M acetic acid was added
dropwise thereto, and stirred and mixed for 60 minutes (step (ii)). Thereafter, the
mixture was filtered to remove the acetic acid, the obtained residue was put in an
alumina crucible, placed in an electric furnace, and subjected to a heat treatment
for four hours with an electric furnace interior temperature of 1,000°C (step (iii)).
After the heat treatment, the mixture was cooled to 200°C inside the furnace and then
cooled to room temperature in a desiccator (23°C-10%RH) to obtain the spherical crystalline
silica powder of Example 2-1.
[Example 2-2]
[0096] Other than setting the heat treatment conditions in step (i) so as to be 1,000°C
for six hours, the spherical crystalline silica powder of Example 2-2 was obtained
by the same method as in Example 2-1.
[Comparative Example 2-1]
[0097] Other than not carrying out step (iii), the silica powder of Comparative Example
2-1 was obtained by the same method as in Example 2-1.
[Comparative Example 2-2]
[0098] Other than not carrying out step (iii), the silica powder of Comparative Example
2-2 was obtained by the same method as in Example 2-2.
[Comparative Example 2-3]
[0099] A spherical amorphous silica powder ("SFP-30M" manufactured by Denka Co., Ltd., average
particle diameter D
50: 0.68 µm) was used as the silica powder of Comparative Example 2-3 (that is, steps
(i)-(iii) were not carried out).
[Comparative Example 2-4]
[0100] 10 g of the spherical amorphous silica powder of Comparative Example 2-3 was filled
in an alumina crucible and subjected to a heat treatment for four hours with an electric
furnace interior temperature of 1,000°C. After the heat treatment, the mixture was
cooled to 200°C inside the furnace and then cooled to room temperature in a desiccator
(23°C-10%RH) to obtain the silica powder of Comparative Example 2-4. Note that when
the degree of crystallization was measured using the method described later, the silica
powder of Comparative Example 2-4 had the same degree of crystallization as Comparative
Example 2-3, crystallization had not proceeded, and the silica powder had remained
amorphous.
Experiment 3
[Example 3-1]
[0101] Other than setting the heat treatment conditions in step (i) so as to be 1,200°C
for four hours and using 500 ml of 1M nitric acid instead of the acetic acid in step
(ii), the spherical crystalline silica powder of Example 3-1 was obtained by the same
method as in Example 1-1.
[Example 3-2]
[0102] Other than setting the heat treatment conditions in step (i) so as to be 1,100°C
for six hours, using 500 ml of 1M nitric acid instead of the acetic acid in step (ii),
and setting the heat treatment conditions in step (iii) so as to be 1,100°C for four
hours, the spherical crystalline silica powder of Example 3-2 was obtained by the
same method as in Example 1-1.
[Comparative Example 3-1]
[0103] Other than not carrying out steps (ii) and (iii), the silica powder of Comparative
Example 3-1 was obtained by the same method as in Example 3-1.
[Comparative Example 3-2]
[0104] Other than not carrying out steps (ii) and (iii), the silica powder of Comparative
Example 3-2 was obtained by the same method as in Example 3-2.
[Measurement]
[0105] Physical properties were measured by the methods described below for the silica powders
obtained in the examples and comparative examples. The results are shown in Tables
1-3.
(XRD measurement: identification of crystal form in powder, measurement of content
thereof, and measurement of degree of crystallization)
[0106] Using a sample horizontal type multipurpose X-ray diffraction device (product name:
RINT-Ultima IV, manufactured by Rigaku Corporation) as a measurement device, X-ray
diffraction patterns of the powders obtained in the examples and comparative examples
were measured under the following measurement conditions.
X-ray source: CuKα
Tube voltage: 40 kV
Tube current: 40 mA
Scanning speed: 10.0°/min.
2θ scanning range: 10°-80°
[0107] Rietveld method software (product name: Integrated powder X-ray software Jade+9.6,
manufactured by MDI) was used in quantitative analysis of the crystal form. Note that
X-ray diffraction measurement was performed on a sample obtained by adding α-alumina
(internal reference substance) (manufactured by NIST), which is a reference sample
for X-ray diffraction, to the silica powder such that the content of the α-alumina
was 50 mass% (based on the total weight of the spherical crystalline silica powder
after the addition), and the ratio (mass%) of each kind of crystal form was calculated
by Rietveld analysis.
[0108] Tables 1-3 show the ratio of α-quartz crystal as "Qua (wt%)" and show the ratio of
cristobalite crystal as "Cri (wt%)".
[0109] For each crystal, an integral area of a reference crystalline peak and of a crystalline
peak of a fabricated sample were determined, and the ratio of the crystalline areas
was used as the degree of crystallization. That is, the degree of crystallization
was calculated by the following formula.
[0110] Degree of crystallization = integral area of peak of obtained crystalline silica/peak
area of crystalline silica standard substance.
[0111] Tables 1-3 show the ratio of α-quartz crystal as "Qua (wt%)" and show the ratio of
cristobalite crystal as "Cri (wt%)".
(ICP measurement)
[0112] Impurities in the silica powders obtained in the examples and comparative examples
were measured as described below.
[0113] 1.2 ml of 46% hydrofluoric acid and 5 ml of ultrapure water were added to 1.0 g of
the silica powder, and this was dried on a 120°C hotplate. 0.3 ml of 96% sulfuric
acid was added to the obtained residue, and after heating, the liquid component was
rendered to 6 ml to create a measurement sample. Further, the solid component generated
was filtered and recovered, and after heating the filter paper by an electric furnace
at 500°C for two hours, the obtained solid component was subjected to alkaline dissolution
and salt dissolution before being rendered to 6 ml. Thereafter, measurement samples
were analyzed using ICP optical emission spectroscopy (ICP optical emission spectrometer,
product name: CIROS-120, manufactured by Spectro Analytical Instruments GmbH) and
the content of impurities in the spherical crystalline silica powder was measured.
(Coefficient of liner thermal expansion: CTE1, CTE2)
[0114] A liquid-state epoxy resin ("JER 828" manufactured by Mitsubishi Chemical Company)
and a hardening agent (4,4-Diaminodiphenylmethane) were mixed at a weight ratio of
4:1, a silica powder was mixed therein so as to be 40 vol.% thereof, and the mixture
was cured at 200°C for four hours to make a cured body. Thereafter, the cured body
was processed to ultimately obtain a test piece with a size of 4 mm × 4 mm × 15 mm.
[0115] A TMA device (TMA 4000SA manufactured by Bruker Corporation) was used to evaluate
the coefficient of linear thermal expansion.
[0116] For measurement conditions, the temperature increase rate was set at 3°C/min., the
measurement temperature was set at -10°C-270°C, and the atmosphere was set to a nitrogen
atmosphere, and from the obtained results, the coefficient of linear thermal expansion
(CTE1) at or below the glass transition temperature Tg (155-160°C or less) and the
coefficient of thermal linear expansion (CTE2) in a temperature region exceeding the
glass transition temperature Tg (exceeding 160°C) were calculated. The results are
shown in Tables 1-3.
[0117] Note that the coefficients of thermal expansion of a resin composition which did
not have the silica powder mixed therein were 3.4×10
-5 (CTE1) and 9.7×10
-5 (CTE2).
[0118] Fig. 1 shows the thermal expansion behavior measured for test pieces using the silica
powder of the reference example, Example 1-5, Comparative Example 1-1, and Comparative
Example 1-3. As shown in fig. 1, the resin molded article comprising the silica powder
of Example 1-5 demonstrated thermal expansion behavior resembling that of the resin
molded article comprising ground quartz (reference example). The resin molded article
comprising the reference example (ground quartz) and the resin molded article comprising
the silica powder of Example 1-5 have higher coefficients of linear thermal expansion
(CTE1 and CTE2) than the resin molded article comprising the silica powder of Comparative
Example 1-1 (spherical amorphous silica powder). When the silica powder of Comparative
Example 1-3 (having spherical cristobalite crystal; not including α-quartz crystal)
is used, although the coefficient of linear thermal expansion is high, changes in
reflow temperatures (240-260°C) are large and there are cases in which it is difficult
to adjust the thermal expansion behavior of the resin molded article near this temperature.
In contrast thereto, in the resin molded article comprising the silica powder of Example
1-5, there is not a large change in the coefficient of linear thermal expansion near
the reflow temperature, and therefore, it is easy to control the thermal expansion
behavior of the resin molded article.
(Evaluation of dielectric properties)
[0119] The silica powder and a polyethylene resin powder (product name: Flo-thene
® UF-20S, manufactured by Sumitomo Seika Chemicals Co., Ltd.) or a polypropylene (PP)
powder (Flow-blen QB200, manufactured by Sumitomo Seika Chemicals Co., Ltd.) were
weighed so that the filled content of the silica powder was 40 vol.% and mixed using
a vibration mixer (manufactured by Resodyn Corporation) with an acceleration rate
of 60 G and a processing time of two minutes to obtain a resin composition. The obtained
resin composition was loaded, at an amount such that the thickness thereof was approximately
0.3 mm, into a metal frame with a diameter of 3 cm and was rendered into a sheet by
a nanoimprinting device (product name: X-300, manufactured by SCIVAX Corporation)
under conditions of 30,000 N and 140°C for five minutes. The obtained sheet was cut
into 1.5 cm × 1.5 cm sizes to obtain evaluation samples.
[0120] Next, a 36 GHz cavity resonator (manufactured by Samtech. Co., Ltd.) was connected
to a vector network analyzer (product name: 85107, manufactured by Keysight Technologies),
an evaluation sample was arranged so as to cover a 10 mm-diameter hole provided in
the cavity resonator, and a resonance frequency (f0) and an unloaded Q value (Qu)
were measured. The same measurement was repeated five times with the evaluation sample
being rotated 90 degrees after each measurement. Average values of the obtained f0
and Qu values were used as measured values and analytical software (software manufactured
by Samtech. Co., Ltd.) was used to calculate the dielectric constant from f0 and the
dielectric tangent (tan δc) from Qu. Note that measurements were carried out in conditions
with a measurement temperature of 20°C and a humidity of 60%RH.
(Number of desorbed water molecules)
[0121] An area value in a 50°C-1,000°C range in a mass chromatogram (m/z=18) was measured,
the mass chromatogram having been obtained by using a Pyrolyzer GC/MS system (comprising
a combination of a gas chromatography mass spectrometer (JMS-Q1500GC) manufactured
by JEOL Ltd. and a multi-shot pyroloyzer (EGA/PY-3030D) manufactured by Frontier Laboratories,
Ltd.), and increasing the temperature from 25°C to 1,000°C at 30°C/min. The number
of desorbed water molecules was calculated from the measured area value by drawing
a calibration curve with aluminum hydroxide (manufactured by Kojundo Chemical Lab.
Co., Ltd.) as a standard substance with a known amount of dehydration.
[0122] In calculating the amount of dehydration of the aluminum hydroxide used as the standard
substance, the amount of decrease in specific gravity from 200° to 320°C using a thermogravimetric
differential thermal analysis device (high-sensitivity simultaneous thermogravimetric
differential balance STA 2500 Regulus, manufactured by Netzsch) and increasing the
temperature from 25°C at 10°C/min. was used as the amount of dehydration.
(Measurement of thermal conductivity)
[0123] The thermal conductivity of the resin composition was calculated by multiplying thermal
diffusivity, specific gravity, and specific heat. After being cured, a sample sheet
was processed to 10 mm × 10 mm × 1 mm and thermal diffusivity was determined by a
laser flash method. A xenon flash analyzer (product name: LFA 447 NanoFlash, manufactured
by Netzsch) was used as the measurement device. The specific gravity was determined
by using the Archimedes method. The specific heat was determined by using a differential
scanning calorimeter (product name: Q2000, manufactured by TA Instruments) and increasing
the temperature from room temperature to 200°C at a temperature increase rate of 10°C/min.
in a nitrogen atmosphere.
[TABLE 1]
|
Step (i) |
Step (ii) |
Step (iii) |
XRD |
EGA-MS |
ICP |
Coefficient of linear thermal expansion (10-5/K) |
Resin sheet |
Specific surface area |
Thermal conductivity |
Raw material amorphous spherical silica D50: 4.5 µm |
Ratio (molar ratio) |
Firing conditions |
Acid wash (acid used) |
Temp (°C) |
Time (h) |
Qua |
Cri |
Degree of crystallization |
No. of water molecules |
CaO amount (oxide conversion) |
Al amount |
CTE1 |
CTE2 |
SiO2 |
CaCO3 |
Temp (°C) |
Time (h) |
(wt%) |
(wt%) |
(%) |
(µmol/g) |
(µg/g) |
(ppm) |
× 10-5/K |
× 10-5/K |
Dielectric constant (ε r) |
Dielectric dissipation factor (tan δ) |
BET(m2/g) |
W/(m*K) |
Example 1-1 |
100 |
3 |
1000 |
12 |
Acetic acid |
1000 |
4 |
46.8 |
0 |
46.8 |
3.3 |
8000 |
530 |
3.8 |
10.7 |
2.76 |
6.3.E-04 |
1.7 |
0.584 |
Example 1-2 |
1200 |
4 |
57.5 |
1.7 |
59.2 |
3.1 |
6000 |
510 |
3.9 |
10.7 |
2.65 |
5.7.E-04 |
1.2 |
0.642 |
Example 1-3 |
100 |
5 |
Acetic acid |
1100 |
4 |
74.4 |
0 |
74.4 |
3.5 |
4000 |
590 |
3.8 |
10.6 |
2.89 |
59E-04 |
1.5 |
0.698 |
Example 1-4 |
1200 |
4 |
77.3 |
3.2 |
80.5 |
3.5 |
5000 |
520 |
3.9 |
10.7 |
2.68 |
6.1.E-04 |
1.2 |
0.720 |
Example 1-5 |
100 |
3 |
1200 |
24 |
Nitric acid |
1000 |
4 |
50.5 |
29.3 |
79.7 |
3.2 |
3000 |
1100 |
4.1 |
10.9 |
2.84 |
6.2.E-04 |
1.3 |
0.754 |
Comp Ex 1-1 |
- |
- |
- |
- |
- |
- |
- |
1.48 |
0 |
1.48 |
38.2 |
32 |
580 |
3.4 |
9.7 |
2.81 |
8.4.E-04 |
2.3 |
0.458 |
Comp Ex 1-2 |
- |
- |
- |
- |
- |
1000 |
4 |
1.48 |
0 |
1.48 |
5.5 |
30 |
560 |
3.4 |
9.7 |
2.69 |
4.7.E-04 |
2.2 |
0.471 |
Comp Ex 1-3 |
100 |
1 |
1300 |
4 |
- |
- |
- |
0 |
95.6 |
95.6 |
3.5 |
900 |
4000 |
4.6 |
11.8 |
2.62 |
1.3.E-03 |
- |
0.760 |
Ref Ex 1 (ground quartz) |
- |
- |
- |
- |
- |
1000 |
4 |
100 |
0 |
100 |
- |
60 |
610 |
3.9 |
10.8 |
2.84 |
3.5.E-04 |
- |
0.948 |
[TABLE 2]
|
Step (i) |
Step (ii) |
Step (iii) |
XRD |
EGA-MS |
ICP |
Coefficient of linear thermal expansion (10-5/K) |
Resin sheet |
Specific surface area |
Thermal conductivity |
Raw material amorphous spherical silica D50: 0.68 µm |
Ratio (molar ratio) |
Firing conditions |
Acid wash (acid used) |
Temp (°C) |
Time (h) |
Qua |
Cri |
Degree of crystallization |
No. of water molecules |
CaO amount (oxide conversion) |
Al amount |
CTE1 |
CTE2 |
SiO2 |
CaCO3 |
Temp (°C) |
Time (h) |
(wt%) |
(wt%) |
(%) |
(µmol/g) |
(µg/g) |
(ppm) |
× 10-5/K |
× 10-5/K |
Dielectric constant (ε r) |
Dielectric dissipation factor (tan δ) |
BET(m2/g) |
W/(m*K) |
Comp Ex 2-1 |
100 |
3 |
1100 |
12 |
Acetic acid |
|
|
38.5 |
34.5 |
73 |
18.2 |
3000 |
160 |
4.1 |
11 |
2.75 |
1.4.E-03 |
4.7 |
0.732 |
Example 2-1 |
100 |
3 |
1100 |
12 |
1000 |
4 |
37.9 |
35.6 |
73.5 |
82 |
2800 |
140 |
4.1 |
11.1 |
2.69 |
6.2.E-04 |
4.5 |
0.754 |
Comp Ex 2-2 |
100 |
3 |
1000 |
6 |
Acetic acid |
|
|
31.1 |
8.1 |
39.2 |
21.5 |
3200 |
170 |
3.8 |
10.6 |
2.84 |
1.5.E-03 |
5.1 |
0.548 |
Example 2-2 |
100 |
3 |
1000 |
6 |
1000 |
4 |
30.8 |
8.5 |
39.3 |
8.5 |
2400 |
180 |
3.9 |
10.7 |
2.68 |
5.9.E-04 |
5 |
0.576 |
Comp Ex 2-3 |
- |
- |
- |
- |
- |
- |
- |
0 |
0 |
0 |
36.1 |
10 |
150 |
3.4 |
9.7 |
2.69 |
1.1E-03 |
6 |
0.439 |
Comp Ex 2-4 |
- |
- |
- |
- |
- |
1000 |
4 |
0 |
0 |
0 |
17.4 |
10 |
160 |
3.4 |
9.7 |
2.78 |
6.6.E-04 |
5.9 |
0.452 |
[TABLE 3]
|
Step (i) |
Step (ii) |
Step (iii) |
XRD EGA-MS |
ICP |
Coefficient of linear thermal expansion (10-5/K) |
Resin conversion sheet |
Specific surface area |
Thermal conductivity |
Raw material amorphous spherical silica D50: 4.5 µm |
Ratio (molar ratio) |
Firing conditions |
Acid wash (acid used) |
Temp (°C) |
Time (h) |
Qua |
Cri |
Degree of crystallization |
No. of water molecules |
CaO amount (oxide conversion) |
Al amount |
CTE1 |
CTE2 |
SiO2 |
CaCO3 |
Temp (°C) |
Time (h) |
(wt%) |
(wt%) |
(%) |
(µmol/g) |
(µ g/g) |
(ppm) |
× 10-5/K |
× 10-5/K |
Dielectric constant (ε r) |
Dielectric dissipation factor (tan δ) |
BET(m2/g) |
W/(m*K) |
Example 3-1 |
100 |
3 |
1200 |
4 |
Nitric acid |
1000 |
4 |
45.0 |
35.9 |
80.85 |
3.1 |
4000 |
3200 |
42 |
11.1 |
2.84 |
6.2.E-04 |
1.5 |
0.739 |
Comp Ex 3-1 |
- |
- |
- |
45.0 |
35.9 |
80.85 |
17.2 |
28000 |
2600 |
4.2 |
11.1 |
2.90 |
1.5.E-03 |
1.5 |
0.719 |
Example 3-2 |
100 |
3 |
1100 |
6 |
Nitric acid |
1100 |
4 |
65.1 |
19.0 |
84.10 |
3.3 |
5000 |
2100 |
4 |
10,7 |
2.83 |
6.8.E-04 |
1.4 |
0.770 |
Comp Ex 3-2 |
- |
- |
- |
65.1 |
19.0 |
84.10 |
17.8 |
24000 |
1200 |
3.9 |
10.7 |
2.89 |
1.7.E-03 |
1.5 |
0.757 |
[0124] As shown in Tables 1-3, the spherical crystalline silica powders of the examples
in which the number of desorbed water molecules is 10 µmol/g or less and 10 mass%
or more of the total powder is α-quartz crystal all enabled a resin molded article
having high coefficients of linear thermal expansion (CTE1 and CTE2) and a low dielectric
tangent to be obtained. Further, the obtained resin molded articles have a high dielectric
constant and a high thermal conductivity. Furthermore, the coefficient of linear thermal
expansion (CTE2) is approximately the same as that of the reference example (ground
quartz), and therefore, the thermal behavior of the resin molded article near the
reflow temperature can be controlled easily.
[0125] In contrast thereto, results show that the amorphous silica powders of Comparative
Example 1-1 and Comparative Example 2-3, in which the number of desorbed water molecules
exceeds 10 µmol/g and in which less than 10 mass% thereof is α-quartz crystal, have
low coefficients of linear thermal expansion and a high dielectric tangent.
[0126] The results also show that although the amorphous silica powders of Comparative Example
1-2 and Comparative Example 2-4, in which less than 10 mass% thereof is α-quartz crystal,
have a low dielectric tangent, the coefficients of linear thermal expansion (CTE1
and CTE2) are low.
[0127] The results further show that in the crystalline silica powder of Comparative Example
1-3 which does not comprise α-quartz crystal, the coefficient of linear thermal expansion
is a high value but the dielectric tangent is high. As shown in Table 1, in the silica
powder of Comparative Example 1-3, there is a large change in the thermal expansion
behavior of the resin molded product near the reflow temperature, and therefore, it
is difficult to control the thermal expansion behavior of the resin molded article.
[0128] The results show that in the silica powders of Comparative Examples 2-1, 2-2, 3-1,
and 3-2, in which the number of desorbed water molecules exceeds 10 µmol/g, the coefficients
of linear thermal expansion are high values but the dielectric tangent is high.
[0129] Focusing on thermal conductivity, the spherical crystalline silica powder of each
of the examples could realize a high thermal conductivity of 0.48 W/mK or more. As
is clear from Tables 1-3, it was discovered that thermal conductivity improves as
a raw material amorphous spherical silica goes through a process comprising being
crystallized (step (i)), and further, being brought into contact with an acid and
subjected to a heat treatment (steps (ii) and (iii)).
INDUSTRIAL APPLICABILITY
[0130] As described above, the spherical crystalline silica powder according to the present
invention has a characteristic of enabling a resin molded article having a high coefficient
of linear thermal expansion and a low dielectric tangent to be obtained. A resin molded
article comprising such a spherical crystalline silica powder can, for example, be
suitably used as a sealing material filler of a semiconductor element.